Slip control method and arrangement for a driveline including a continuously variable transmission

ABSTRACT

A slip control method and arrangement for a driveline including a continuously variable transmission is described herein. The driveline includes a clutch that is so controlled as to slip when a torque higher than the usable torque attempts to pass through. Accordingly, the clutch prevents the prime mover from stalling.

FIELD

The present disclosure generally relates to drivelines including acontinuously variable transmission (CVT). More specifically, the presentdisclosure is concerned with a slip control method and arrangement forsuch a driveline.

BACKGROUND

CVTs are very interesting in all kinds of vehicles for their ability tocontinuously vary the speed ratio between the output of a prime moverand the wheels or other rotating parts of a vehicle.

However, some vehicular applications conventionally require a so-calledtorque converter between the prime mover and the wheels to a) preventthe prime mover from stalling when the wheels are prevented fromrotating while powered and b) increase the torque when the torqueconverter is slipping. These applications are generally not idealcandidates for continually variable transmissions since the advantagesof the CVT are mitigated from the use of a torque converter.

There is therefore a need to provide a method and arrangement preventingthe prime mover from stalling and multiplying the torque when the wheelsare partially or totally prevented from rotating.

BRIEF DESCRIPTION OF THE DRAWINGS

In the appended drawings:

FIG. 1 is a block diagram of a driveline including a CVT and a slipcontrol arrangement according to an illustrative embodiment;

FIG. 2 is a block diagram of a method to control the slip of a clutch;and

FIG. 3 is a graph illustrating the torque vs. RPM of a prime mover andthe torque allowed to pass through a clutch vs. RPM.

DETAILED DESCRIPTION

An object is generally to provide an improved driveline including a CVT.More specifically, an object is to provide a slip control method andarrangement used in a driveline including a CVT to reduce the risks ofthe prime mover stalling.

More specifically, in accordance with an aspect of the slip controlmethod and arrangement for a driveline including a continuously variabletransmission, there is provided a method to control the slippage of adriveline including a prime mover having an output shaft, a continuouslyvariable transmission having an input connected to the output shaft ofthe prime mover and an output, a clutch having an input connected to theoutput of the continuously variable transmission and an output; theclutch having a controllable slippage level between its input andoutput, and a load connected to the output of the clutch, the slippagecontrol method including:

determining the usable torque of the prime mover; and

controlling the slippage level of the clutch so as to allow the usabletorque to pass therethrough and to cause the clutch to slip should atorque between the input and output of the clutch be greater than theusable torque.

According to another aspect, there is provided a driveline including:

a prime mover having an output shaft;

a prime mover speed sensor measuring the rotational speed of the outputshaft;

a CVT having an input associated with the output shaft of the primemover and an output;

a clutch having an input associated with the output of the CVT and anoutput;

a clutch slip controller controlling the level of torque allowed to passthrough the clutch before slippage occurs therein; and

a main controller associated with the prime mover speed sensor and withthe clutch slip controller; the main controller being so configured asto determine a usable torque of the prime mover and to set the clutchslip controller so that the clutch slips when a torque higher than theusable torque attempts to pass through the clutch.

The use of the word “a” or “an” when used in conjunction with the term“comprising” in the claims and/or the specification may mean “one”, butit is also consistent with the meaning of “one or more”, “at least one”,and “one or more than one”. Similarly, the word “another” may mean atleast a second or more.

As used in this specification and claim(s), the words “comprising” (andany form of comprising, such as “comprise” and “comprises”), “having”(and any form of having, such as “have” and “has”), “including” (and anyform of including, such as “include” and “includes”) or “containing”(and any form of containing, such as “contain” and “contains”), areinclusive or open-ended and do not exclude additional, unrecitedelements or process steps.

The expression “connected” should be construed herein and in theappended claims broadly so as to include any cooperative or passiveassociation between mechanical parts or components. For example, suchparts may be assembled together by direct connection, or indirectlyconnected using further parts therebetween. The connection can also beremote, using for example a magnetic field or else.

The term “about” is used to indicate that a value includes an inherentvariation of error for the device or the method being employed todetermine the value.

It is to be noted that the expression “prime mover” is to be construedherein and in the appended claims as an internal combustion engine (ICE)a turbine engine, or any other mechanical power production element orassembly.

It is to be noted that the term “CVT”, standing for ContinuouslyVariable Transmission, is used herein to describe any type of CVTincluding, amongst others, a toroidal CVT, a dual-cavity full toroidalCVT, a half-toroidal CVT, a single cavity toroidal CVT, a hydrostaticCVT, a Variable diameter pulley CVT, a magnetic CVT, a ratcheting CVTand a cone CVT.

It is to be noted that the expression “overdrive” when used in thecontext of a CVT, is to be construed herein and in the appended claimsas a condition where the CVT ratio is such that the CVT output speed ishigher than the CVT input speed. The CVT ratio (of output speed to inputspeed) is therefore higher that one to one (1:1).

It is to be noted that the expression “underdrive” when used in thecontext of a CVT, is to be construed herein and in the appended claimsas a condition where the CVT ratio is such that the CVT output speed islower than the CVT input speed. The CVT ratio (of output speed to inputspeed) is therefore lower that one to one (1:1).

It will also be noted that the expressions “fixed disk”, when usedherein and in the appended claims in the context of clutch technology,may be viewed as any element or group of elements constituting a clutchdriving member. Similarly, the expressions “movable disk”, when usedherein and in the appended claims in the context of clutch technology,may be viewed as any element or group of elements constituting a clutchdriven member.

It is to be noted that the expression “off-highway vehicle” is to beconstrued herein and in the appended claims as any type of vehicle thatis designed specifically for use off-road, including, amongst others,construction vehicles and agricultural vehicles.

Other objects, advantages and features of the slip control method andarrangement for a driveline including a continuously variabletransmission will become more apparent upon reading of the followingnon-restrictive description of illustrative embodiments thereof, givenby way of example only with reference to the accompanying drawings.

FIG. 1 of the appended drawings illustrate a driveline 10 comprising aprime mover in the form of an ICE 12, a CVT 14, a clutch 16 and anoptional synchro 18. The output of the optional synchro 18 is connectedto a load 20, for example wheels of an off-road vehicle. Of course,should the optional synchro 18 be absent from the design, the output ofthe clutch 16 would be connected to the load 20.

A first shaft 22 interconnects the output of the ICE 12 and the input ofthe CVT 14; the speed of the first shaft is measured via a first speedsensor 24. A second shaft 26 interconnects the output of the CVT 14 andthe input of the clutch 16; the speed of the second shaft 26 is measuredvia a second speed sensor 28. A third shaft 30 interconnects the outputof the clutch 16 and the input of the optional synchro 18; the speed ofthe third shaft 30 is measured via a third speed sensor 32. Finally, afourth shaft 34 interconnects the output of the optional synchro 18 andthe load 20.

Of course, as mentioned hereinabove, one skilled in the art willunderstand that should the synchro 18 be absent, the shaft 34 would notbe present and the shaft 30 would interconnect the output of the clutch16 and the load 20.

Conventionally, the ICE 12 is associated with a user throttle control36, for example an acceleration pedal (not shown).

The driveline 10 includes a ratio controller 38 so configured as to setthe ratio of the CVT 14 according to either a ratio provided by the uservia a user ratio control 40 or according to a ratio provided by a maincontroller 42 as will be described hereinbelow. It will be understoodfrom the foregoing description that the ratio supplied by the maincontroller 42 has precedence over the user ratio control 40.Accordingly, the main controller 42 may take over and dictate the ratioof the CVT 14.

A clutch controller 44 is so configured as to take a usable torque valuefrom the main controller 42 and to control the clutch 16 so as to slipwhen the torque attempting to pass through is greater than this usabletorque. In other words, when the torque between the input and output ofthe clutch 16 is greater than the usable torque, the clutch 16 slips.

One skilled in the art will have no problem building such a clutchcontroller adapted to the technology used in the clutch 16.

The speed data from the first and second speed sensors 24 and 28 issupplied to the main controller 42 so that the controller 42 maydetermine the actual ratio of the CVT in real time. Furthermore, thespeed data of the second and third speed sensors 28 and 32 is suppliedto a slip detector 46 that may determine if slippage of the clutch 16occurs, in real time, and supply this data to the main controller 42.

As shown in the appended drawings, the synchro 18 and its connection tothe main controller 42 are optional and shown schematically. Thissynchro 18 is there to represent a conventional multi speed arrangementthat allows different gear ratios to be interposed between the clutch 16and the load. Since the configurations and the operation of such asynchro are believed known to those skilled in the art, they will not befurther described herein.

Turning now to FIG. 2 of the appended drawings, a slip control method100 for a driveline including a continuously variable transmission willbe described.

The first step 102 of the method 100 consists of determining theavailable torque from the prime mover. With reference to FIG. 1, theprime mover, in the form of the ICE 12, has a map of available torquedepending on the RPM of its output shaft. This table is either built inthe ICE and can be supplied to the controller 42, known and stored inthe controller 42 or has been built by the driveline manufacturer andstored in the controller 42. Since the controller 42 has the speed datafrom the first speed sensor 24, it can look up the available torque inreal time.

FIG. 3 of the appended drawings illustrates the available torque vs. RPMfor a particular ICE.

From the instantaneous available torque, the controller 42 determines ausable torque in step 104. The usable torque is lower than the availabletorque and provides a safety margin to prevent the ICE 12 from stalling.

Again, FIG. 3 illustrates the usable torque vs. RPM for a particularICE. It is to be noted that the usable torque does not follow theavailable torque at low RPMs. The reason therefore will be explainedhereinbelow.

It is to be noted that the usable torque illustrated in FIG. 3 is theusable torque at the output of the ICE 12. The use of a CVT 14downstream of the ICE allows this usable torque to be modified by theCVT 14. Indeed, the torque is multiplied as a function of the ratio ofthe CVT. The controller therefore uses its knowledge of theinstantaneous ratio of the CVT 14 to determine a usable torque at theinput of the clutch 16 and this value is used in the next steps. Inother words, the usable torque graph of FIG. 3 is offset as a functionof the CVT ratio by the controller 42.

It is to be noted that the usable torque values can be stored in alook-up table provided in the main controller 42, for example.Accordingly, the controller 42 may quickly determine the usable torquefrom the speed of the output of the ICE 12.

The controller 42, in step 106, supplies the instantaneous usable torqueto the clutch controller 44 that controls the clutch 16 so that slippageof the clutch 16 occurs if a torque greater than the usable torqueattempts to pass therethrough. Accordingly, should a block load beapplied, for example by preventing wheels of the off-road vehicle fromturning, the torque requested by the wheels and therefore attempting topass through the clutch 16 increases drastically and quickly exceeds theusable torque. When this occurs, the clutch 16 slips, preventing the ICEfrom stalling and protecting the various components of the driveline,including the CVT 14. Indeed, as is well known to those skilled in theart, should the output shaft of the ICE be prevented from rotating whilethe ICE is operating, the ICE would stall. Slippage of the clutch 16above a torque level therefore ensures that the output shaft of the ICEis not prevented from rotating.

The method 100 could stop there. It would therefore loop back to step102 and repeat the above-described steps.

However, since the driveline 10 includes a CVT that can inherentlymodify the speed ratio and therefore the available torque at the inputof the clutch 16, supplemental steps may be added to the method 100 toimprove the usability of the driveline 10.

Step 108 involves the determination of the slippage level of the clutch16. This is done by the slip detector 46 and the slippage data issupplied to the main controller 42.

The controller 42, in step 110, branches to step 112 if the clutchslippage is non-null. In other words, if there is slippage, step 112 isperformed.

In step 112, the controller 42 takes over the ratio control 38 anddictates the ratio of the CVT 14. The controller 42 is so configuredthat the ratio of the CVT is decreased in proportion of the slippage ofthe clutch 16. Indeed, since the usable torque increases as the CVTratio decreases, the slippage setpoint of the clutch 16 is automaticallymodified by the controller 42 and slippage may stabilize, decreaseand/or stop.

One possible way of controlling the driveline 10 is to control theclutch slippage so as to stabilize it. This is done by graduallychanging the CVT ratio until the clutch slippage remains substantiallyconstant.

Step 112 loops back to step 102.

Should no slippage be detected in step 110, the step 114 is performed.In this step, the control of the CVT ratio is gradually returned back tothe user since the usable torque is sufficient to drive the load 20.This is done gradually so as to prevent sudden change in drivingbehavior, which is detrimental to the user driving sensations.

The performance of the driveline may be controlled by the user in thosecircumstances. This step returns to step 102 to loop the method 100.

Returning to FIG. 3, the usable torque graph may be separated in threezones. A low RPM zone 202, a medium RPM zone 204 and a high RPM zone206.

In the low RPM zone 202, the usable torque is set significantly lowerthan the available torque. Accordingly, the slippage of the clutch 16will be more pronounced at these speeds. In this zone, the usable torqueis set low enough as to either prevent rotation of the output or allow“creeping” of the output given a small load depending on the desireddriving sensation.

In the medium RPM zone 204, the usable torque linearly increases withthe RPM but is still significantly lower than the available torque fromthe prime mover. The clutch slippage set-point will therefore increasewith increasing RPM. Accordingly, should a small block load preventrotation of the wheels, an increase in RPM (while in the zone 204) maycause the wheels to rotate. This has been found to give better drivingsensations to the operator. Of course, the linearity of the medium RPMzone is not required and other functions could be used.

Finally, in the high RPM zone 206, the usable torque follows theavailable torque with a safety margin.

As an example of application of the driveline 10, the operation of aloader tractor will be briefly described. Such a tractor often has topush against obstacles, for example when its bucket is being filled.When this is the case, the ICE must be prevented from stalling. Byproviding a driveline as proposed herein, the ICE stalling would beprevented by the selective slipping of the clutch and the torquesupplied to the wheels would be increased by the control of the CVTratio. All that without special intervention of the operator other thanactuating the throttle control according to the desired speed of thevehicle.

Of course, a clutch pedal or other user control could be used todisengage the clutch 16 manually by the operator.

As will be easily understood by one skilled in the art, the maincontroller 42 could integrate the ratio controller 38, the clutchcontroller 44 and/or the slip detector 46.

It is to be understood that the slip control method and arrangement fora driveline including a continuously variable transmission is notlimited in its application to the details of construction and partsillustrated in the accompanying drawings and described hereinabove. Theslip control method and arrangement for a driveline including acontinuously variable transmission is capable of other embodiments andof being practiced in various ways. It is also to be understood that thephraseology or terminology used herein is for the purpose of descriptionand not limitation. Hence, although the slip control method andarrangement for a driveline including a continuously variabletransmission has been described hereinabove by way of illustrativeembodiments thereof, it can be modified, without departing from thespirit, scope and nature thereof.

What is claimed is:
 1. A method to control the slippage of a drivelineincluding a prime mover having an output shaft, a continuously variabletransmission having an input connected to the output shaft of the primemover and an output, a clutch having an input connected to the output ofthe continuously variable transmission and an output; the clutch havinga controllable slippage level between its input and output, and a loadconnected to the output of the clutch, the slippage control methodincluding: determining the usable torque of the prime mover; andcontrolling the slippage level of the clutch so as to allow the usabletorque to pass therethrough and to cause the clutch to slip should atorque between the input and output of the clutch be greater than theusable torque.
 2. The slippage control method of claim 1, wherein theusable torque determining includes determining an available torque ofthe prime mover according to an instantaneous speed of an output shaftof the prime mover and calculating a usable torque at the instantaneousspeed of the prime mover.
 3. The slippage control method of claim 1further comprising: detecting a slippage level of the clutch; settingthe CVT ratio as a function of the slippage level of the clutch so as toincrease the usable torque.
 4. The slippage control method of claim 1further including integrating the driveline to an off-highway vehicle.5. A driveline including: a prime mover having an output shaft; a primemover speed sensor measuring the rotational speed of the output shaft; aCVT having an input associated with the output shaft of the prime moverand an output; a clutch having an input associated with the output ofthe CVT and an output; a clutch slip controller controlling the level oftorque allowed to pass through the clutch before slippage occurstherein; and a main controller associated with the prime mover speedsensor and with the clutch slip controller; the main controller being soconfigured as to determine a usable torque of the prime mover and to setthe clutch slip controller so that the clutch slips when a torque higherthan the usable torque attempts to pass through the clutch.
 6. Thedriveline recited in claim 5, wherein the usable torque is determined asa function of the rotational speed of the output shaft of the primemover.
 7. The driveline recited in claim 5, further comprising means todetect slippage in the clutch and a ratio controller setting theoutput/input ratio of the CVT; wherein the ratio controller decreasesthe CVT ratio when slippage is detected.
 8. The driveline recited inclaim 7, wherein the slippage detecting means include an input speedsensor measuring the speed of the clutch input and an output speedsensor measuring the speed of the clutch output.
 9. The drivelinerecited in claim 5, further comprising a user control to manuallydisengage the clutch.
 10. The driveline recited in claim 7, wherein theratio controller and the clutch slip controller are integrated with themain controller.
 11. The driveline recited in claim 5, where thedriveline is integrated in an off-highway vehicle.